A variable star, as its name suggests, is a star whose magnitude varies intrinsically, in contrast to eclipsing binaries whose magnitude
varies as a result of one star in the binary system eclipsing the other. True variables are one of five types, namely Mira stars, semiregular
stars, cepheids, eruptive variables and, finally, cataclysmic variables. Minimum to maximum magnitude can range from days to many months with
some variables displaying irregular periods.
A popular method for the study of variable stars, particularly short-term variables, is by the use of the technique known as "differential
photometry". Rather than measure the (variable) magnitude of a variable star on an absolute scale, measurements are made over time relative to
one or more non-variable star(s) and these differences are then plotted so as to study and illustrate the relative or differential change in
magnitude. Due to the very large number of variables stars, the field of differential photometry represents one of the key fields in astronomy
whereby the amateur astronomer can make a meaningful and long-lasting contribution to both science and astronomy.
More recently, the search for extrasolar planets (over 300 discovered so far) has identified yet another interesting application for the
practice of differential photometry whereby the minute drops in magnitude of a star hosting an exoplanet are studied. Further details for the
interested party are available here.
Note: The eclipsing binary star BL Cam is one of the fastest variables known with a period of 56.30 minutes and
which involves a change of 0.33 magnitudes during this very brief time interval. Further details from the General Variable Star Search Gateway
are available here whereas an AAVSO
finder chart is available
here.
Variable Star: BL Cam Other Designation: GSC 4067:471 RA / Dec: 03h 47m 20s / +63° 22' 43" Magnitude: 12.92 - 13.25 Period: 0.03909760 days Variability: SXPHE Check Star: GSC 4067:77 Comparison Star: GSC 4067:283 |
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Date: Nov 25, 2008 20:19 - 21:35 UT+2 Location: Athens, Greece Equipment: AP 160 f/7.5 Starfire EDF AP 1200GTO GEM SBIG ST-10XME SBIG CFW10 SBIG LRGB filters Integrations:
Temperatures:
Software: CCDSoft V5.00.188 AIP4Win V2.2 Processing: Reduction Differential Photometry |